Process for making heating elements



Oct. 14, 194 1. E. K. CLARK 2,259,242

PROCESS FOR MAKING HEATING ELEMENTS Filed Feb. 18, 1939 2 Sheets-Sheet lWITNESSES: INVENTOR 560 K. C/ar/f.

ATTORNEY 41 Patented Oct. l4, 3941 Earl K. Clark, Mansfield inghouseElectric'& East Pittsburgh, Pa. vania Ohio, assignor to West-Manufacturing Company, a corporation of Pennsyl- Application February18, 1939, Serial No. 257,167

2 Claims.

My invention relates to electric heaters and more particularly tomethods of making a preformed ceramically insulated heater for aflatiron or the'like.

The general process of compacting a cementitious or refractoryinsulating material about an electrical resistor is well known to theart. However, due to the application of considerable pressure upon theinsulating material during the process, it has been practicallyimpossible to produce an unsheathed heater in which the resistor isformed from a helical coil. This difflculty has been caused by the coilshifting under the compactin'g pressure. Further, it has beenpractically impossible to get a uniform distribution of the insulatingmaterial inside the coil. In addition, the difliculties of getting theinsulating material within a coiled resistor are considerably increasedwith a heating element formed in an elliptical helical manner,especially so, when the long axis 01' the helix is mounted in a verticalposition.

It is, therefore, an object of my invention to provide a method ofmaking a heating element having an ellipticallycoiled resistor and auniformly compacted cementitious insulating material located within andabout such coil.

A further object of my invention is to provide a method of making apreformed ceramical- 1y insulated heater for flatirons, or the like,which eliminates the necessity of handling cement in the vicinity of thefinished and polished iron sole plate.

A further object of my invention is to provide a method of producing aheating element having a ceramic insulating material pressed around acoiled resistor without distorting such resistor.

Another object of my invention is to provide method of producing aceramically insulated heater in which the resistor is mechanicallyretained within the insulationso as to he centraliy located therein andwhich will not shift its peeltion'upon applying the final compactingpressure.

' Still another object of my invention is to provide an efficient,economical method of producing a ceramically insulated gore-formed fitiron heater and of measuring the quantity 1nsulating material required.

'Qther objects of invention will either pointed out specifically in thecourse of the following description of a method of forming a deviceembodying my invention, or will be apparent from such description. A

the accompanying drawings:

plate in which a heating element embodying my invention is located.

Fig. 2 is a partial elevational and sectional view of an illustrativepress for making the heating element embodying my invention;

Fig. 3 is a perspective view of the heating elewith insulating materiall8, compacting the inbody portion, a

Figure 1 a perspective view of a z'iatircn sale sulating material,invertin structure and placing additional insulating material upon theouter side of the resistor, and finally compacting the whole heatingelement.

More specifically, the die structure l3 comprises, in this instance, afirst stripper plate or holding device i l, main forming dies 29 and 22,

a second stripper plate 24 and a pressure die 2G which is adapted to beinserted between the forming dies 20 and 22 and within. the slot it.

The first stripper plate it comprises a main plurality of upwardlyextending bosses 28 and an upwardly extending holding portion 30. 1eupwardly extending bosses 28 cooperate with recessed portions 3! themain forming dies 28 and 22, so as to pcsition and retain such formingdies in a given fixed location and an upwardly extending holding portion30. The upwardly extending holding portion 3t is substantially the sameshape as one-half of the heating element in to he formed and is adaptedto extend upwardly between the main forming dies 28 and 22 withintheslct 36 formed therebetween. The forming dies .20 and 22 are thusretained in a given position and. in conjunction with holding portionSi), determine the configuration of the heating element to be formed. Inthis in stance, the slot therebetween is approximately the same shape asthe slot 53 the flat-iron scieplate 55.

The upwardly plate H has a grooved slot 32 located substantially in themiddle of the upper surface thereof. The grooved slot 32 issubstantially the same Width as the external minor axis of theelliptically coiled resistor 2 and has a depth substantially one-halfthe external major axis of holding portion 38 of the stripper suchresistor.- The groove 32 is thus capable of retaining the resistor I! ina vertical position at substantially the middle of the slot l6 andpermits only substantially the upper half of the resistor to be exposedfor a purpose hereinafter described. However, it is to be understoodthat the resistor B? may be retained within the die structure by anyother suitable holding device.

The vertically extending slot it formed between the forming dies 28 and22 is substantially the same width and approximately the same shape asthat desired of the finished heater iii. However, the vertical height ofsuch slot is considerably greater than that of the height of thefinished heater it. In this instance, the height of the slot i6 is ofsuch value as to permit it to be used as a measuring device for theinsulating material to be placed therein, substantially as hereinafterdescribed.

The second or other stripper plate 2 3, located at the bottom of the diestructure in Figs. 6 and 7, is substantially the same shape as the firststripper plate or holding device it and has a plurality of bosses 2Qwhich cooperate within corresponding apertures 33 within the dies 25 and22, and a holding portion 36.

The holding portion 3% of the second stripper plate '25 portion 3B ofthe lower stripper plate 53. However, holding portion 3 3 of plate 2 3is substantially as long as the distance the pressure die 28 extendsinto the slot it during the first compacting operation. Accordingly, itis obvious that after the pressure die 26 has compacted the firstportion of cementitious insulating material placed within the slot it,the upper stripper plate 25 may be located upon the forming dies 20 and22 with the holding portion 3 3 contactin the flat upper surface of thecompacted insulating material, substantially as hereinafter described.

The pressure plate die 28 of the die structure i3 has a downwardlyextending die portion 36: which is substantially the same shape as theslot i6 soas to freely extend therein as the die is forced downwardly.

The die structure it may be operatively associated with a pressureapplying device or press 38 which is illustratively shown in Fig. 2. Thepress 38 includes a base plate 69 and a vertically movingpressure-applying member 52. The pressure device or press 38 is adaptedto supply a relatively large pressure to the cementitious insulatingmaterial located within the slot it by means of the pressure die 26which is rigidly attached to the vertically moving member 42. The

base plate in has an undercut or depressed portion 4| which issubstantially the same shape as the stripper plates M and 2 1. Thisportion Bi thus permits the plates it and 25 to be accurately centeredthereon with respect to the pressure die 26.

The cementitious refractory ceramic insulating heater I is constructedin accordance with my invention substantially as follows: the diestructure I3 is operatively associated with the pressure device 38 byhaving the pressure die 26 attached to the vertically moving member 42and by having the first stripper plate M located and centered upon thebase plate 40 within the depressed portion M. The main forming diesand'22 are then positioned upon the first plate l4, whereupon thevertically extending slot {6 is located therein (see Fig. 2). Theelliptically coiled resistor i2 is then positioned within the issomewhat shorter than the holding groove 32 upon the holding portion 30of the holding device I4 in the slot Hi. The resistor I2 is thuspositioned at substantially the midpoint of the slot it with the mainaxis thereof located in a vertical position. The cementitious ceramicinsulating material I8 is then put in and just fills the slot [6, theslot it thus acting as a measuring device. In other words, theinsulating material i8 is located within the slot it so as to just fillsuch slot (see Fig. i). Inasmuch as the insulating material issubstantially in a powdered form it is obvious that such material willbe evenly disposed within the loosely coiled resistor and aboutthe upperportion thereof.. The pressure device 38 is then actuated so that themoving member 52 thereof will force the pressure die 2% downwardly. Thedie portions 35 thereof will then enter into the slot i8, engaging theinsulating material It and preliminarily compacting it into a-relativelysolid mass. Inasmuch as the insulating material is evenly distributedwithin and around the upper portion of the resistor 52, it is obviousthat the pressure applied to the insulating material it will then evenlycompact it to a uniformly dense mass within the resistor l2 and aboutthe upper portion thereof (see Fig. 5).

The grooved slot 32 located in the holding portion 30 of the firstholding device it being substantially the same shape as the lower halfof the resistor i2, retains the resistor in a fixed vertical position,during the compacting step, insuring a uniform distribution of thecompacted insulating material entirely within the coils of the resistorand limits the amount of insulating material being located about theouter surface of the coil.

In this instance, the horizontal plane of the top face of holdingportion 38, which determines the lowermost point of the insulatingmaterial it prior to and during the first compacting step is positionedat substantially the mid-point of the vertical or major axis of theresistor 82 (see Figs. 5 and 6). In addition, the material is locatedwithin the coils of the resistor i2. However, the insulating materialplaced upon and within the resistor during the first step of productionneed not completely fill the resistor, and the dividing line need not bepositioned exactly as described so long as the compacted material iscapable of retaining the coil in a fixed position during the remainingsteps of the process.

The pressure die 26, by reason of the movable action of the movingmember i2 is then removed from the main forming dies 20 and 22. Thesecond stripper plate 24 is then located or positioned upon the mainforming dies 29 and 22 with the holding portion 35 extending into theslot It and resting upon the upper surface of the compacted insulatingmaterial i8. The die structure 83 including the second and firststripper plates 24 and it, respectively, and the main forming dies 20and 22 is then reversed or inverted so that th upper strip or plate 2twill be located at the bottom of the main forming dies 28 and 22. Theupper or second stripper plate will then be positioned within thedepressed portion 6i so as to'again center the slot is with respect todie 26.

The lower or first stripper plate it, which is now on top, is thenremoved, leaving the now upper portion of the slot l8 open (illustratedas 5a in Figs. 6 and 7). Additional insulating material I8 is thenpositioned within and just filling the exposed portion of the slot it,which therein; but when at this stage is located again acts as ameasuring device for the amount of insulating material'required. Theloose. uncompacted cementitious refractory insulating material Ila isthen located upon the previously compacted insulating material I. andabout the now upper or remaining portion of the resistor i2. However,inasmuch as the inner space of the coil II has been previouslysubstantially filled and compacted with insulating material, thenewlyadded insulating material Ila cannot extend the coil II has been onlypartially filled the additional or second portion of insulating materialwill fill the remaining space within such coil. The vertically movingpressure applying member 42 is then moved downwardly, causing the dieportion 36 of the pressure die member ftto extend into the slot i andcompact the additional insulating material Ila (see Fig. 7).

The final compacting pressure in the step just described issubstantially greater than the preliminary compacting pressure in thestep previously described, inasmuch as the resistor I! was alreadyfirmly positioned within the compacted material I8 and will not movewith respect to the outer edge thereof even though a relatively highpressure is applied. Accordingly, it follows, that the final pressureapplication may be of such value as to safely and satisfactorily.

compact the insulating material into a solid homogeneous mass about andwithin the helically coiled resistor.

It is to be understood that the coiled resistor may be of any desiredshape other than the preferred elliptical section used herein. it is tobe understood that the insulating material used in thefirst compactingstep is to be located within as well as about the coils of such resistorso as to allow the resistor to be retained in a given fixed position.while the initial pressure or compacting step'is effected. v

After having had sufiicient pressure applied thereto, the main formingdies II and .22 are removed from the second stripper plate 24, which atthe bottom. The heating unit it may then be moved fromthe holding givenfixed position, the insulating material isevenly distributed throughoutthe heater, and

However,

because of the even distribution of insulating material, afin'alcompacting pressure may be applied which will form a solid homogeneousinsulating mass about and within the resistor without causing theresistor to shift therein.

It therefore follows that by using the two-step compacting processembodying my invention in which the resistor is centered and held inposition until firmly embedded in the first portion of insulatingmaterial, such element, after having the second portion of insulatingmaterial placed thereon, may be subjected to a second pressuresubstantially greater than the first without causing the resistor toshift its-position, In other words the process embodying my inventionprovides a method for centering and holding the resistor within theinsulating material and elimihating electrical insulating faults in thefinal product.

Various modifications may be made in the method of forming the deviceembodying my invention without departing from the spirit and scopethereof, and I desire, therefore, that only such limitations imposed bythe prior art and the appended claims.

-I claim as my invention:

1. The method of making an electrical heating element in which theresistor; is in the form of a helical coil, which comprises encompassinga portion of the helical coil below a horizontal longitudinal planetherethrough to hold the coil in place, placing uncompacted insulatingmaterial within the entire coil but around only the unencompassedportion of the coil above said plane, compacting the insulating materialaround said unencompassed portion of the coil, inverting the coil andfreeing the encompassed portion thereof, placing uncompacted insulatingmaterial around the freed and now upper portion, and compacting theadditional insulating material.

2. The method of making a heating element inadditional material.

. EARL K. CLARK shall be placed thereon as are

